Highly recommended. Lets you document concepts and logical types, as opposed to only the physical types. This is in contrast to Doxygen, which focuses on the physical types. Also, the comments in the code (where you read them most of them time) are much less cluttered and look more natural than with other systems.
On the minus side, unlike Doxygen it does not do full syntax parsing of C++; and the fact that each function has a prototype and a definition creates duplicate topics if you document both. Also, single-file PDF documentation cannot be generated (though you could use some tool to convert the HTML website to a single PDF).
On balance, this is my documentation system of choice. Many thanks to the author, hope he continues improving it.